Dual stage instrument for scanning a specimen

ABSTRACT

A dual stage scanning instrument includes a sensor for sensing a parameter of a sample and coarse and fine stages for causing relative motion between the sensor and the sample. The coarse stage has a resolution of about 1 micrometer and the fine stage has a resolution of 1 nanometer or better. The sensor is used to sense the parameter when both stages cause relative motion between the sensor assembly and the sample. The sensor may be used to sense height variations of the sample surface as well as thermal variations, electrostatic, magnetic, light reflectivity or light transmission parameters at the same time when height variation is sensed. By performing along scan at a coarser resolution and short scans a high resolution using the same probe tip or two probe tips at fixed relative positions, data obtained from the long and short scans can be correlated accurately.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/730,641,filed Oct. 11, 1996, which is a continuation-in-part of application Ser.No. 08/598,848, filed Feb. 9, 1996, now abandoned, which is acontinuation-in-part of application Ser. No. 08/362,818, filed Dec. 22,1994, now U.S. Pat. No. 5,705,741, entitled “Constant-Force Profilometerwith Stylus-Stabilizing Sensor Assembly, Dual-View Optics, andTemperature Drift Compensation,” referred to hereinafter as the “parentapplication.” This application is filed on the same day as theapplication entitled “System for Locating a Feature of a Surface,”referred to hereinafter as the “companion application.”

BACKGROUND OF THE INVENTION

This invention relates in general to instruments for scanning samples orspecimens and in particular to a system for scanning samples orspecimens with improved characteristics.

Profiling instruments were first developed for the purpose ofcharacterizing surfaces in terms of roughness, waviness and form. Inrecent years, they have been refined for precise metrology in themeasurement and production control of semiconductor devices. Profilinginstruments are also used outside the semiconductor industry, forexample, for scanning and sensing optical disks, flat panel displays,and other devices.

Stylus profilometers for use in the above-mentioned applications havebeen available from Tencor Instruments of Mountain view, Calif., andother manufacturers. In a conventional stylus profilometer, a sample isplaced on an X-Y positioning stage, where the surface of the sample tobe measured or sensed defines the X-Y plane. The stylus profilometerincludes a stylus tip brought to a position relative to the sample tosense certain interactions between the stylus tip and the surface of thesample. The stylus and stylus tip are attached to an elevator whichmoves in a Z direction that is perpendicular to the X-Y plane. Thesensor does not move in X or Y directions (i.e., directions in the planeparallel to the surface of the sample). The interactions between thestylus tip and the sample are measured by the sensor. In a dataacquisition sequence, the X-Y stage moves the sample in a controlledmanner under the stylus tip while the sensor senses variations ofsample-stylus tip interactions across the sample surface as the sensorscans the sample surface. Thus during data acquisition using the sensor,the X-Y stage is moving the sample in a controlled manner.

The Alpha-step® is another type of stylus profilometer available fromTencor Instruments of Mountain view, Calif. The Alphastep scans a sampleby moving a stylus arm across the sample.

Thus stylus profilometers provide for scans in the X-Y plane fordistances ranging from a few microns to hundreds of millimeters. Thesensors used for profilometers usually have large dynamic range as well.For example, in stylus profilometers for sample height measurements,vertical variations in the Z direction as small as a few Angstroms to aslarge as a few hundred micrometers can be detected. Significantly, theheight measurement profilometer measures height directly.

As the semiconductor industry has progressed to smaller dimensions witheach new generation of products, there is an increasing need forscanning instruments that can repeatably scan samples to a very fineresolution. The large size of the X-Y stage in the stylus profilometerlimits the lateral positioning resolution of the conventional stylusprofilometer. Thus the repeatability of X-Y repositioning of stylusprofilometers is limited to about 1 micrometer; such device lacks thecapability for repeatable nanometer or sub-nanometer X-Y positioningcapability.

It is therefore desirable to provide an improved scanning instrumentthat can provide better X-Y repeatable positioning resolution than theconventional stylus profilometer, while retaining many of theprofilometer's advantages, such as wide dynamic range in the Z directionand long scan capability up to hundreds of millimeters.

It is desirable for semiconductor wafer surfaces to be flat or planar.To achieve such global planarization, Chemical Mechanical Polishing(CMP) is employed. CMP processing is typically applied after tungstenplugs, via holes have been fabricated on the surfaces of thesemiconductor wafers. If the CMP processing is not functioning properly,it may cause a recess in the tungsten plug or via hole and, therefore,affect the size and depth of the tungsten plugs and via holes. This maylead to a variation of capacitance and electrical resistance across thesurface of the semiconductor wafer which adversely affect the operationof electronic circuits fabricated on the wafer. The problem becomesparticularly accute in vary large scale integration circuits where thesize of transistors and other electronic devices have been continuallyreduced. This is true also for laser textured hard disks.

To monitor the functioning of CMP processing, scanning probe microscopesand profilometers have been used. While profilometers are able toprovide a measure of the surface topography of the wafer, conventionalprofilometers lack the resolution to discover the shape and depth of thetungsten plugs or via holes, for example. Thus, if the profilometer scandid not pass over the tungsten plug or the via hole, information fromthe scan would not reveal such information. Conventional profilometerslack the position/positioning capability to allow precise alignment ofsubmicron features with the scan. Hence, if profilometers are used formonitoring the CMP process, even though the global planarization of thesample and the relative height of points that are spaced apart on thewafer can be monitored, a precise local morphology of the surface cannotbe measured.

While scanning probe microscopes (SPMs) do have the precisionpositioning capability to allow precise alignment of submicron featureswith the scan path, SPM devices do not have a precise long range andrepeatable motion, so that it is difficult to use SPM devices to findout the relative locations of two points that are spaced far apart onthe wafer surface or the height relationship between two tungsten plugsor via holes that are spaced apart on the wafer. As a matter of fact, inmany SPM devices, any tilt experienced by the devices is considered asbackground and is subtracted. Even if a number of local images acquiredby the SPM are stitched together, the global topography of the surfaceis lost, and height differences between points that are spaced that arespaced apart by distances beyond the range of SPM devices cannot beprecisely measured. Moreover, data correlation between a number of localimages of the SPM is cumbersome, time consuming and requires significantduplication of resources.

It is, therefore, desirable to provide an improved system which avoidsthe above-described difficulties.

SUMMARY OF THE INVENTION

This invention is based on the observation that by including a finestage having a resolution much finer than that of the conventional X-Ypositioning stage used for the stylus profilometer, positioningresolution can be much improved while retaining all of the advantages ofthe conventional stylus profilometer. A positioning stage withcharacteristics similar to the conventional X-Y positioning stage usedin the stylus profilometer will be referred to below as the coarse stageas opposed to the fine stage. A fine stage is defined as a positioningstage with resolution better than that of the coarse stage.

In the preferred embodiment and at the time of this application, acoarse stage means one that can position a sensor to an accuracy of, atbest, about 100 Angstroms, and a fine stage is defined as one that canposition the sensor at an accuracy better than 100 Angstroms. As knownto those skilled in the art, as technology advances, the dividing linebetween a coarse stage and a fine stage, namely 100 Angstroms, may becontinually reduced. Such coarse and fine stages with improvedresolution employed in the manner described herein are also within thescope of the invention.

A first aspect of the invention is directed towards an instrument forsensing a sample, comprising a sensor for sensing a parameter of thesample, a coarse stage causing relative motion between the sensor andthe sample, a fine stage causing relative motion between the sensor andthe sample, and at least one controller controlling the two stages sothat either one or both of the two stages cause relative motion betweenthe sensor and the sample when the sensor is sensing a parameter of thesample.

Another aspect of the invention is directed towards a method for sensinga sample, comprising the steps of causing relative motion between asensor and the sample by means of a coarse stage, causing relativemotion between the sensor and the sample by means of a fine stage, andsensing a parameter of the sample when relative motion between thesensor and the sample is caused by each of the two stages.

Yet another aspect of the invention is directed towards an instrumenthaving a finer lateral resolution than a conventional profilometer butretains the wide dynamic range of the conventional profilometer in thevertical direction. Such instrument comprises a sensor for sensing aparameter of the sample, where the sensor includes a stylus arm having astylus tip for sensing a surface parameter of the sample, a hingesupporting the stylus so that the stylus arm is rotatable about thehinge and means for applying a force to the stylus arm. The instrumentfurther includes a fine stage causing relative motion between the sensorand the sample, said fine stage having a resolution of 1 nanometer orbetter.

Still another aspect of the invention is directed towards a method formeasuring one or more features of a surface, comprising the steps of (a)scanning a first probe tip of a profilometer or scanning probemicroscope along a first scan path over the surface and sensing a firstfeature to provide first data on the first feature; and (b) scanning asecond probe tip of a profilometer or scanning probe microscope of thefirst probe tip along at least a second scan path over the surface andsensing at least one second feature to provide second data on the atleast one second feature, said second path being shorter than the firstscan path. The resolution of the sensing during the second scanning stepis higher than that during the first scanning step. One more aspect ofthe invention is directed towards an apparatus for measuring a sample,comprising two sensors, one suitable for use in the profilometer, andthe other in a scanning probe microscope; in coarse stage for causingrelative motion between the two sensors and the sample; and a fine stagefor causing relative motion between the two sensors and the samples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a dual stage scanning instrument toillustrate the preferred embodiment of the invention.

FIG. 2 is a block diagram of a dual stage scanning instrument and itscontrol and display system to illustrate the preferred embodiment of theinvention.

FIG. 3A is a schematic view of a height sensor connected to apiezoelectric tube serving as the fine stage of a dual stage scanninginstrument to illustrate a first embodiment of the fine stage and sensorassembly.

FIG. 3B is a perspective view of a height sensor and two piezoelectrictubes serving as the fine stage to illustrate the second embodiment ofthe fine stage and sensor assembly.

FIG. 4A is a side perspective view of a sensor assembly employing amagnetic means for causing a stylus tip to apply a desired force to asample to illustrate the preferred embodiment of the invention.

FIG. 4B is a cross-sectional view of a portion of the sensor assembly ofFIG. 4A.

FIG. 4C is an end perspective view showing details of the magneticstylus force biasing means of the sensor assembly of FIG. 4A.

FIG. 4D is a block diagram of the electronics for stylus forceadjustment according to the present invention.

FIG. 4E is a schematic diagram of a sensor assembly employing acapacitative means for causing a stylus tip to apply a desired force toa sample to illustrate another embodiment of the invention.

FIG. 5 is a schematic diagram of a dual stage scanning instrument wherethe sample is supported by the fine stage and the sensor is supported bythe Z portion of the coarse stage to illustrate another embodiment ofthe invention.

FIG. 6 is a schematic diagram of a sensor that can be used in a dualstage scanning instrument of this application to illustrate oneembodiment of the sensor.

FIGS. 7A-7C are schematic diagrams of a sensor of the type shown in FIG.6, by showing different embodiments of the deflection sensor portion.

FIG. 7D is a schematic diagram of a probe portion to illustrate anotherembodiment of the proximity sensor of FIG. 7C.

FIGS. 8A-8C are schematic drawings of the sensor of the type shown inFIG. 6, by showing different embodiments of the secondary sensor in moredetail.

FIG. 9 is a schematic diagram of a stylus tip that may be used toimplement the sensor of FIG. 8A.

FIG. 10 is a cross-sectional view of a stylus tip which can be used toimplement the sensor in FIG. 8B.

FIG. 11 is a top view of a deflection sensor made from a planar sheet ofmaterial to illustrate the preferred embodiment of the invention.

FIG. 12 is a top view of a portion of a fine stage employingpiezoelectric stacks to illustrate the invention.

FIG. 13 is a schematic view of a path of scanning of a sample surfacefollowed by a sensor in a dual stage scanning instrument to illustratethe preferred embodiment of the invention.

FIG. 14 is a block diagram of a surface measurement system useful forillustrating the invention of the companion application.

FIG. 15 is a schematic view of a target area of a surface having afeature and search paths thereon to illustrate the method for locatingthe feature of the invention of the companion application.

FIG. 16 is a schematic view of a target area of a surface and searchpaths thereon illustrating a method for searching the feature of FIG. 15to illustrate the invention of the companion application.

FIG. 17 is a schematic view of a target area of the surface having afeature and search paths thereon illustrating a method of the inventionof the companion application.

FIG. 18 is a representative cross-sectional view of a feature of thesurface to illustrate the invention of the companion application.

FIGS. 19A-19I are schematic views of a target area of a surface having afeature therein and search paths thereon to illustrate a method forsearching the feature as the preferred embodiment of the invention ofthe companion application.

FIGS. 20A-20C are schematic views of a target area of a surface having afeature therein and search paths thereon to illustrate a searchingmethod employing an intermittent contact mode in combination withcontact or non-contact mode for illustrating another embodiment of theinvention of the companion application.

FIG. 20D is a schematic view of a larger and a smaller target area of asurface having a feature therein and search paths thereon in both targetareas to illustrate searching method for illustrating yet anotherembodiment of the invention of the companion application. The method canbe used in contact mode, non-contact mode or intermittent contact mode.

FIGS. 21A-21C are cross-sectional views of a surface and intermittentsearch paths to illustrate another embodiment of the invention of thecompanion application.

FIG. 22 is a schematic view of a target area of a surface and searchpaths thereon illustrating a searching method employing a sequence ofrandom locations for finding the approximate location of the feature anda non-random algorhithm for locating the feature boundary once theapproximate location of the feature has been located for illustratingstill another alternative embodiment of the invention of the companionapplication.

FIG. 23 is a schematic view of a spiral search path on a surface forsearching a feature on or in a surface to illustrate still anotheralternative embodiment of the invention of the companion application.

FIG. 24 is a schematic view of a substantially rectilinear spiral searchpath for locating the feature of a surface to illustrate one morealternative embodiment of the invention of the companion application.

FIG. 25 is a schematic view of a serpentine search path for locating thefeature of a surface to illustrate still one more alternative embodimentof the invention of the Companion application.

FIG. 26 is a schematic diagram of a conventional scanning probemicroscope useful for illustrating the invention.

FIG. 27 is a schematic view of a dual stage scanning instrumentincluding a scanning probe microscope sensor as well as a profilometersensor where both sensors are mounted on the same fine X-Y stage toillustrate yet another embodiment of the invention.

FIG. 28 is a schematic view of a dual stage scanning instrument with thetwo sensors of FIG. 27 but where only the scanning probe microscopesensor is mounted onto a fine stage to illustrate one more embodiment ofthe invention.

FIG. 29A is a schematic view of a profile of a surface scanned over twopoints AA, BB to illustrate the invention.

FIGS. 29B and 29C are local high resolution profiles of the surface ofFIG. 29A at high resolution to show the local profile at the points AAand BB, respectively.

FIG. 30 is a schematic view of a scanning operation where a long scan istaken over a surface as well as a number of short scans, some of whichintersect the long scan and where at least one short scan is in thevicinity of but does not intersect the long scan to illustrate theinvention.

FIG. 31 is a schematic view of a scan path that includes a number ofsubstantially parallel scan line segments to illustrate the pattern ofscanning for either the long scan or the short scan to illustrate theinvention.

FIG. 32 is a schematic view of a scan path where the same scanninginstrument is used to perform a long scan between a starting point andan end point as well as short local scans at a starting point and endpoint to illustrate a preferred embodiment of the invention.

FIG. 33 is a schematic view of a scan path performed in the vecinity ofa number of points on the surface as well as local scans at such pointsto illustrate another embodiment of the invention.

FIGS. 34A-34E are schematic views of a profile and of three localfeatures as well as their relative heights to illustrate the invention.

For simplicity in description, identical components in the differentfigures of this application are identified by the same numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic view of a dual stage scanning instrument 100 toillustrate the preferred embodiment of the invention. Since the sensorassembly 60 may be much lighter than the sample or specimen 90, it maybe desirable to support the sensor by means of the fine stage 70 and usethe XY portion 80 b of the coarse stage 80 to support the specimen orsample. The fine stage is in turn connected to and supported by the Zportion 80 a of the coarse stage. Thus, as shown in FIG. 1, the scanninginstrument 100 includes a sensor assembly 60 connected to and supportedby a fine stage 70 which in turn is connected to and supported by the Zportion 80 a of the coarse stage 80. A sample 90 is supported by the XYportion 80 b of the coarse stage 80. The Z portion 80 a and X-Y portion80 b of coarse stage 80 are connected to and supported by base 102 asshown in FIG. 1.

Fine stage 70 preferably has a lateral resolution of about 1 to 50Angstroms (0.1 to 5 nanometers),although a lateral resolution of 100 oreven 1000 Angstroms (10 or 100 nm) may be adequate for someapplications. The lateral resolution of the coarse stage 80 ispreferably about 50 to 100 Angstroms (5 to 10 nanometers) and a verticalresolution of about 10 to 50 Angstroms (1 to 5 nanometers), although alateral and vertical resolution of 1 micrometer may be adequate for someapplications.

The coarse stage has a scan range of about 1 micrometer to hundreds ofmillimeters, such as 500 millimeters. While the fine stage has a scanrange of about 0.01 to 500 micrometers, this is compensated for by thecoarse stage so that the dual stage instrument 100 has a scan range ofabout 0.01 micrometer to hundreds of millimeters, such as 500millimeters. This will be illustrated in more detail below. Sensor 60 isof a type that has a dynamic range that can accommodate the verticaldynamic range of the coarse stage, or at least about 500 micrometers.

Instrument 100 can be used in a number of modes for sensing samples.Thus instrument 100 can be used in the same manner as a conventionalprofilometer. By deactivating the fine stage 70, the coarse stage 80 canbe used in the same manner as a conventional profilometer for scanningsample 90 by means of sensor assembly 60. This is possible since sensorassembly 60 has an adequate dynamic range to accommodate possible largevariations in the height of a surface of sample 90 over a long scan thatcan be as long as hundreds of millimeters.

Another possible mode of operation is to use the coarse stage to movethe sensor assembly 60 while sensing the sample in a manner similar tothat of a conventional profilometer to locate an area of interest of thespecimen or sample 90, while the fine stage is deactivated. After suchan area has been located, the coarse stage can be deactivated and thefine stage activated and used to scan the area of interest at highresolution. In other words, the two stages may be used sequentially tomove the sensor while a sample parameter is being sensed.

Yet another possible mode of operation is to operate both the fine stage70 and the coarse stage 80 substantially simultaneously and the sensorassembly 60 is used to sense a parameter of the sample 90 while bothstages are substantially simultaneously causing relative motion betweenthe sensor assembly and sample 90. Thus the X-Y portion 80 b of thecoarse stage may be used to move the sample along the X axis while thefine stage 70 is used to move the sensor assembly 60 along the Y axis.While both stages are causing relative motion between the sensorassembly and the sample, the sensor assembly 60 may be used to sense oneor more parameters of sample 90. In this manner, since the X-Y portionof the coarse stage 80 is stationary in the Y direction, the resolutionof the fine stage 70 would control when the sensor assembly 60 sensesthe parameter of the sample along the Y direction. Then to obtain thesame resolution along the X direction, the X-Y portion 80 b of thecoarse stage may be used to move the sample along the Y direction butremain stationary along the X direction, while the fine stage is used tomove the sensor assembly 60 along the X direction but remain stationaryalong the Y direction. In this manner, fine resolution can be achievedalong both the X and Y directions. Further modes of operation will bedescribed in more detail below.

FIG. 2 is a block diagram of a dual stage scanning instrument and itscontrol and display system to illustrate the invention. FIG. 2 need tobe modified only slightly for controlling ther embodiments of theinstrument, such as the one shown in FIG. 5.

As shown in FIG. 2, the fine stage 70 is controlled by a fine stagecontrol 110. The Z portion 80 a of the coarse stage is controlled by thecoarse Z control 112 and the X-Y portion 80 b of the coarse stage ascontrolled by a coarse X-Y control 114. The sensor assembly 60 andsample 90 are controlled by a sensor/sample control 116. Thus,control116 may apply a voltage to a sample with controlled frequency andamplitude, or an electrical signal may be sensed from the sample. Astorage device 118 is used for storing the data from the sensor assembly60. The storage device 118 also receives XYZ positioning informationfrom controls 110, 112, 114, 116, so that the parameter of the samplesensed can be correlated with the XYZ position of the sensor assembly60, and therefore to particular locations of the sample 90. Systemcontroller 120 is used to control the overall system and for providinginformation to a monitor 122 for display. Thus the parameter sent byassembly 60 together with the positioning information from controls 110,112, 114, and 116 may be processed on the fly by system controller 120and displayed; alternatively, such data may be stored in storage device118 and processed and displayed at a later time. System controller 120and the controls 110, 112, 114, and 116 are used to enable assembly 60to perform various operations as described below. Implementation of thecontrols 110, 112, 114, 116, and 120 based on their functions asdescribed herein is routine and known to those skilled in the art.

FIGS. 3A, 3B, and 5 illustrate different embodiments of the fine andcoarse stages and of the sensor assembly 60. FIG. 3A is a perspectiveview of one embodiment of the fine stage and of the sensor assembly. InFIG. 3A, the fine stage 70′ includes a piezoelectric tube 132. Theembodiment of FIG. 3B differs from that of FIG. 3A in that the finestage 70″ includes two piezoelectric tubes 132 instead of one. The sameembodiment 60′ of the sensor assembly is shown in FIGS. 3A, 3B, 4A, and5. The construction of one embodiment 60′ of sensor assembly 60 and theoperation thereof described below in reference to FIGS. 4A-4D are takenessentially from the parent application.

With reference to FIG. 4A, a diamond stylus tip 11 having a radius of0.01 mm or less is adhered to an end of a slender stainless steel wire13 which is bent at a right angle. The wire radius is about 0.25 mm. Thediamond tip is adhesively mounted to a squared-off end of the wire 13,while the opposite end of the wire 13 is inserted into an elongatedhollow aluminum arm 15 which has a length of approximately 2 cm and awall inside radius of approximately 0.018 cm. The aluminum arm issufficiently rigid that it will not bend when sensing step heights, yetsufficiently low mass that its moment of inertia can be kept low. Theoverall mass of the arm, wire and diamond tip should preferably notexceed approximately 0.05 grams. Arm 15 fits into a support block 19 andis operably connected to flexural pivot 21, which also fits into supportblock 19. In this manner, the aluminum arm 15 has a center of rotationabout the flexural pivot 21. The flexural pivot 21 has enough torsion tolightly hold the stylus tip 11 downwardly against a surface to bemeasured, such as specimen or sample 10. The entire mass on the stylusside of the pivot should preferably not exceed 0.50 grams, including alever 59 described below.

An electrical solenoidal coil 51 is comprised of wire coil 53 around aplastic bobbin 50. The wire used is preferably thousands of turns offine copper wire. The coil 51 becomes magnetized on application ofcurrent by means of wires 55, seen in FIG. 4B. The magnetized coil 51attracts a ferromagnetic tip of an aluminum lever 59. The lever 59 hasan end opposite the ferromagnetic tip which is affixed to the supportblock 19. The ferromagnetic tip is preferably a magnet that is made of amaterial that is very hard magnetically and has a very strong field forits sized, such as a neodymium-iron-boron magnet. A magnet 57 is shownin a holder 52 attached to the end of lever 59 opposite support block 19in FIGS. 4A-4C. Lever 59 is preferably curved so that magnet 57 may bepositioned directly above flexural pivot 21. By applying current to thewires 55 and magnetizing the coil 51, magnetic force is exerted on thelever 59 causing a force bias in the form of a pull toward or away fromthe center of coil 51. The lever 59 should be lightweight, yet stiff sothat the lever will not bend on the application of magnetic force. Themagnet 57 and magnetic coil 51 are part of the stylus force biasingmeans of the present invention.

Variations in the force exerted as the magnet 57 moves may be minimizedand the magnitude of the force maximized by placing the magnet 57 nearthe position of the peak magnetic field gradient, i.e., on the axis ofthe coil 51 and proximate to the plane of the end of the coil winding.In the preferred embodiment of the invention, the magnet 57 is spacedapart from the coil winding 51 to prevent it from traveling inside thecenter bore of the coil. At its closest position, magnet 57 is nearlytouching the coil 51. The placement of magnet 57 allows for easyadjustment of the position 0f the magnet. Alternatively, magnet 57 canbe positioned so that it enters the center bore of the coil 51. Thisallows the magnet's range of travel to be centered on the peak of themagnetic field gradient, but requires precise alignment of the magnet 57with the coil 51.

The use of a very powerful material for the magnet 57, such as aneodymium-iron-boron material, allows the magnet to be very small andlight in weight and to still generate useful amounts of force. In thepreferred embodiment, the magnet is 3 mm in diameter and 1.5 mm thick.The corresponding low current requirement minimizes the power dissipatedin the coil, which minimizes the heat generated. This in turn minimizesthe thermally-induced expansion and contraction of the materialscomprising the sensor assembly. These thermally-induced size changes cancause undesirable drift in the measured profile of the sample orspecimen.

In the preferred embodiment, the underside of a support body 71 hasattached a transducer support 72 which acts as an elevational adjustmentfor a pair of spaced-apart parallel capacitor plates 35 and 37. Thespacing between the plates is approximately 0.7 mm, with an air gapbetween the plates. A small spacer, not shown, separates plate 35 fromplate 37 and a screw fastens the two plates to transducer support 72.The area extent of the plates should be large enough to shield the vane41 from outside air, so that the vane experiences resistance to motiondue to compression of air momentarily trapped between the closely spacedplates. A pair of electrical leads 39 of FIG. 4B is connected to theparallel plates, one lead to each plate. Between the parallel plates, alow mass electrically conductive vane 41 is spaced, forming a capacitorwith respect to each of the parallel plates 35 and 37. The range ofmotion of the vane, indicated by arrows A in FIG. 4B, is plus or minus0.16 mm. Moreover, vane 41, being connected to the support block 19 andflexural pivot 21, damps pivoting motion as the vane attempts tocompress air between the parallel plates. This damping motion of thevane serves to reduce vibration and shock which may be transmitted intoarm 15. Vane 41 is connected to a paddle 43 which is the rearwardextension of support block 19, opposite stylus arm 15, serving tocounterbalance the arm. The total mass of the vane, paddle and pivotmember on the vane side of the pivot should preferably not exceed about0.6 g. Movement of the vane between plates 35 and 37 results in changeof capacitance indicative of stylus tip motion. Such a motion transduceris taught in U.S. Pat. No. 5,309,755 to Wheeler.

The illustrated configuration of the support body 71, L-shaped bracket73, and transducer support 72 is intended only as an example of asupport for the sensor stylus assembly of the present invention.Additionally, the stylus displacement measurement means or motiontransducer described and positioned relative to the stylus tip ispreferred, but may be substituted by an equivalent means for indicatingthe stylus tip motion.

In operation, the stylus tip 11 scans a surface to be measured, such asa patterned semiconductor wafer. Scanning may be achieved either bymoving the stylus arm frame with respect to a fixed wafer position oralternatively moving the wafer, on an X-Y positioning wafer stage suchas the fine and/or coarse stages with the position of the stylus fixed,or a combination of the two motions. In the latter instance, the stylusarm may be moved linearly in the X direction while the wafer is advancedin the Y direction after each lengthwise X direction scan. The stylustip 11 is maintained in contact with the surface of the wafer at asteady level of force by an appropriate bias applied through the coil 51into the lever 59. The bias is preferably great enough to maintaincontact, but not great enough to damage the surface being measured.Deflections of the tip 11 are caused by topological variances in thesurface being measured and these are translated rearwardly through theflexural pivot 21 to the vane 41. Vane 41 resists undesirable largeamplitude motion due to vibration because of the air displacementbetween the parallel plates 35 and 37. However, as the air is compressedand displaced, the vane 41 moves slightly causing a signal in electricalleads 39 reflecting a change in an electrical bridge circuit connectedto these wires. At the end of a scan, the tip 11 is raised to protect itfrom damage in the event that a wafer is changed.

In building arm 15, wire 13 and tip 11, it is desirable to maintain themoment of inertia as small as possible. The mass-radius squared productshould preferably not exceed about 0.5 g-cm². The current design has amass-radius squared product of 0.42 g-cm². The radius is measured withrespect to the center of the flexural pivot 21 to the furthest radialextent of the steel wire 13. A similar moment of inertia is calculatedwith respect to the vane 41 and the lever 59. The sum of the moments istermed the moment of inertia for the entire stylus arm. By maintaining alow moment of inertia, the stylus arm is less sensitive to vibration.Greater resolution in profile measurements of thin films, and the like,may therefore be achieved in the preferred embodiment.

The present invention signifies an improvement over the prior artbecause it allows for a dynamic change in the force coil current as thestylus moves vertically, thereby eliminating the stylus forcevariability of previous devices. The instrument of the present inventionmay be calibrated by serving the drive current to move the non-engagedstylus to regularly spaced positions to create a table of positionversus current settings. That table provides the data for a polynomialcurve fit approximation. A digital signal processor 84 of FIG. 4D usesthe curve fit to dynamically change the force setting as the positionmeasurements are taken, with a specimen in place. A positive, constantforce is generated by adding a steady current offset to the fitpolynomial, as a direct fit would result in zero force.

FIG. 4D provides an illustrative block diagram of the above stylus forceadjustment electronics. The electrical signals produced by motiontransducer 81, i.e., vane 41 in conjunction with parallel plates 35 and37, are selected and stored within a signal conditioning circuit 82 forspecified vertical positions, creating data points, while the stylus tip11 is not in engagement with specimen 10. Since the stylus tip issupported by a flexure, i.e., a torsion spring, the data points aredirectly proportional to force levels because of the spring law, F=kx.The signals are then converted to a digital format by converter 83 and adigital signal processor 84 generates a polynomial curve for the datapoints. The curve is then adjusted by processor 84 to represent theforce desired upon stylus tip 11 during profiling. The adjusted curveprovides modulation instructions; i.e, feedback signals, which areconverted to an analog format by converter 85 and signal the circuit 86driving the coil 51 to modulate current 87 within the coil for constantstylus force.

The above description of one embodiment 60′ of the sensor assembly 60 istaken from the parent application. In reference to FIGS. 3A, 3B, and 5,in the event the assembly 60′ is employed, fine stages 70, 70′, 70″,70′″ and the Z portion 80 a of the coarse stage respectively areconnected or attached to the support body 134 of the sensor assembly60′. Another aspect of the invention is directed to a combination of afine positioning stage and the sensor assembly 60′ of FIG. 1. Such acombination has the advantage of fine X-Y or lateral resolution of onenanometer or better while retaining the wide Z or vertical dynamic rangeof the conventional profilometer.

Instead of a magnetic force biasing device shown in FIGS. 4A-4D, acapacitive force biasing device 91 comprising two capacitive plates 93may be used. As shown in FIG. 4E, arm 162 is attached through aconnector 166 a to a deflection plate 95 placed between the two plates93 supported by support 150. A voltage supply (not shown) is used toapply appropriate voltages to the two plates 93 to cause the stylus tip164 to apply a desired variable or constant force to the sample orspecimen. The desired force can be controlled in a manner the same asthe one described above for the magnetic biasing in rerefence to FIG.4D.

In reference to FIGS. 3A and 3B, the piezoelectric tubes 132 each has anaxis 132′. One end of the tube(s) is attached to support plate 134. Whenappropriate voltages are applied to each tube 132, the tube can becaused to bend in a direction perpendicular to its axis 132′ relative tobase plate 134, in order to cause the sensor assembly 60′ to move in anydirection in the X-Y plane. Appropriate voltages can also be applied toeach of the tubes 132 to cause the tube to expand or contract in thedirection parallel to its axis 132′. In this manner, each of the tubes132 can be controlled to move the sensor assembly 60 along the Z axis.The manner in which this can be done is explained in detail in“Single-Tube Three-Dimensional Scanner for Scanning TunnelingMicroscopy,” Binnig and Smith, Rev. Sci. Instrum., 57(8), August 1986,pp. 1688-1689. Therefore, a detailed explanation of how the tubes 132can be controlled to cause motion of assembly 60′ in any direction inthree-dimensional space will be omitted here.

The arc motion of the tube is non-linear and may produce errors in the Zdirection. This can be corrected by using capacitative devices 136 tomeasure the position of the sensor assembly 60′ in the Z direction andfeeding back any z motion to the fine stage control 110. Devices otherthan capacitative devices 136 can also be used as known to those skilledin the art.

Thus as shown in FIGS. 1, 3A, and 3B, the fine stage 70, 70′, 70″ areconnected to a support plate 134 which is in turn attached to the Zportion of 80 a of the coarse stage as shown in FIG. 1. In oneparticular embodiment, the inside and outside surfaces of the tube 132are segmented into quadrants. Different from Binnig and Smith, insteadof applying a voltage only to the outside surfaces of the quadrant,appropriate voltages can also be applied to the inside surfaces of thequadrants. This has the effect of doubling the motion range of the tube.Instead, a shorter tube may be used to achieve the same motion range. Ashorter tube also increases the mechanical resonance frequency of thesensor assembly, which in turn allows faster motion of the fine stage.

The embodiment of FIG. 3B is advantageous over that of FIG. 3A in thatthe weight of the sensor assembly 60′ is distributed over two tubes 132,allowing faster scans and better control of the position of the sensorassembly relative to the surface of a specimen or sample. In theembodiment of FIG. 3B, the sensor assembly 60′ may be connected to thetwo tubes 132 by means of flexular hinges 138 consisting of stainlesssteel vanes.

In some applications, it may be desirable to use the fine stage to movethe sample or specimen. This is shown in FIG. 5. As shown in FIG. 5, thesample 90 is supported by three piezoelectric tubes 132 connected to andsupported by the X-Y portion 80 b of the coarse stage 80. The sensorassembly 60′ is attached directly to a base plate 134 which is attachedin turn to the Z portion 80 a of the coarse stage 80. Both portions ofthe coarse stage are then attached to and supported by the base 102which serves as a fixed reference. In this embodiment, the sensorassembly is moved only by the Z portion of the coarse stage, whereas thesample 90 is moved by both the fine stage 70′″ and the X-Y portion ofthe coarse stage.

FIG. 6 is a schematic diagram of a sensor 60″ which is anotherembodiment of sensor 60′ of FIGS. 1, 2, 3A, 3B, and 5. Sensor 60″differs from sensor 60′ of FIGS. 3A and 3B in that it includes not onlya tip for sensing the height of a surface of a sample, but also asecondary sensor for sensing one or more additional parameters, such asthermal variations or an electrostatic, magnetic, light reflectivity, orlight transmission parameter of the sample or specimen. As shown in FIG.6, sensor assembly 60″ includes a support 150 supporting a height sensor160 and a secondary sensor 170. The height sensor 160 includes a stylusarm 162 having ends 162 a, 162 b and connected to the end 162 a of thearm a stylus tip 164. Height sensor 160 also includes a force controldevice 166 and a deflection sensor 168 for sensing the amount ofdeflection of the stylus arm caused by a variation of height of thesurface of a sample. The deflection sensor may be magnetic or capacitiveas described above in reference to FIGS. 4A-4E. Other deflection sensingschemes may also be used and are within the scope of the invention.

In reference to FIG. 6, the stylus arm 162 is supported rotatably bysupport 150 at hinge 182 so that when the arm is rotated, the end 162 aof the arm has a dynamic range of at least about 500 micrometers. Theforce control 166 preferably comprises a magnetic or capacitive forcebiasing device 166 b as described above and a connector 166 a attachingthe device 166 b to arm 162.

The interactions between the stylus tip 164 and a surface of the samplewould cause arm 162 to rotate about hinge 182. Rotation of arm 162 willcause the back end 162 b to move away from or towards the deflectionsensor 168. Such movement of end 162 b is sensed by the sensor 168 asdiscussed above in order to measure directly the height of the surfaceof the sample.

One particular embodiment of sensor assembly 60″ where the deflectionsensor 168 as a capacitive sensor is illustrated in FIG. 7A. In otherwords, the capacitive sensor 168 a functions in substantially the sameway as sensor 60′ of FIGS. 4A-4D described above. As end 162 b of thearm moves closer to capacitive plate 202 and farther away fromcapacitive plate 204, end or vane 162 b changes the capacitance betweenplates 202, 204, and this will be sensed as indicating a dip on asurface of the sample interacting with tip 164. Motion of end 162 b inthe opposite direction causes a corresponding change in capacitance andwould indicate a hill or an upward slope of a surface interacting withtip 164. As explained in detail above and below in reference to FIGS.4A-4D, 11, force control 166 b can be used to control a force betweenstylus tip 164 and the surface of the sample.

FIG. 7B illustrates another embodiment of sensor 60″ where thedeflection sensor is a linear voltage differential transformer (LVDT)sensor. As shown in FIG. 7B, as end 162 b of the arm moves when the armrotates about the hinge 182, a core 212 attached to end 162 b of the armwould move into or out of the space enclosed by coils 214 of the LVDTsensor. This would cause a change in current through the coils 214 as adirect indication of the height of a surface interacting with stylus tip164.

FIG. 7C is another embodiment of sensor assembly 60″ where thedeflection sensor 168 c comprises a light source 222, an input opticalfiber 224 for delivering light from the light source towards a mirror226 on the top surface of end 162 b of the arm 162. Such light isreflected by the mirror 226 towards a detection optical fiber 228 whichdelivers the reflected light to a photodetector 230. As end 162 b moves,this will cause the amount of light reflected by mirror 226 and capturedby detection fiber 228 and detector 230 to change, thereby againindicating directly the height variations of a surface interacting withstylus 164. The fibers 224, 228 may be bound together for convenience inhandling as shown in FIG. 7D in a support probe body 229. Suitabledevices that can be used for sensor 168 c include the fiber opticproximity sensor from Phone-Or, Ltd. Ashkelon, Israel; and the Series 88fiber-optic displacement sensors from Philtec, Inc. of Arnold, Md.

As shown in FIG. 6, one or more secondary sensors 170 is attached tosupport 150, where the secondary sensor or sensors are placed in suchposition to sense a parameter other than height of the sample at alocation the height of which is sensed by stylus tip 164 and deflectionsensor 168.

FIG. 8A is a schematic diagram of sensor assembly 60″ where thesecondary sensor senses the thermal variations across a sample. Thesecondary sensor comprises a pair of thermal couple wires 252, 254embedded in stylus tip 164. The pair of wires 252, 254 are connected toa thermal couple sensor 256. A more detailed illustration of a portionof the secondary sensor in FIG. 8A is illustrated in FIG. 9.

FIG. 8B is a schematic view of sensor 60″ illustrating one particularembodiment of the secondary sensor. As shown in FIG. 8B, the secondarysensor is an electrostatic sensor comprising an electrically conductivecore 262 surrounded by a conductive shield 264 where the core and theshield are separated by an insulating layer 266 (not shown) and wherethe core, shield and insulating layer are all embedded in the stylus tip164 as shown in FIG. 10. The core is connected through wire 272 and ashield is connected through wire 274 to sensor 276. Therefore, anyelectrostatic charge variations of the sample at the location sensed bystylus tip 164 will be sensed by sensor 276. FIG. 10 illustrates in moredetail the construction of stylus tip 164 with the conductive core 262,conductive shield 264, and insulating layer 266 embedded therein. Thesharp end 268 of the stylus may be formed by the insulating layer orshield 264.

FIG. 8C is another embodiment of sensor assembly 60″ where the secondarysensor comprises a light intensity reflection sensor which includes alight source 302 which supplies light through a half silvered mirror 304to the sample at the location interacting with stylus tip 164. Lightreflected or scattered by the sample at such location is detected by thephotodetector 306 to sense the light reflectivity or scatteringproperties of the sample at the locations at which height variations aredetected. If the photodetector 306 is placed on the opposite side of thesample from the source 302, the sensor arrangement of FIG. 8C may beused to sense light transmission properties instead. Stylus tip 164 usedin this case is preferably transparent.

FIG. 11 is a top view of a sensor assembly 300 illustrating a preferredembodiment of the assembly. The entire sensor assembly may bemanufactured starting with a planar piece of silicon or silicon oxide.By means of conventional techniques used in the semiconductor industry,a plate of silicon or silicon oxide may be etched to form an arm 362having a wider section 362′ and a narrower section 362″At the end of thethinner section 362″ is attached a tip preferably made of diamond.Integral with the arm 362 is a support piece 370 for supporting a forcecoil 372. The support 370 together with the arm 362 are connected to theremainder portion of the plate by means of two hinges 374. The forcecoil may comprise a layer of electrically conductive material depositedor implanted onto the surface of the support 370. Preferably, the layerof material is in the shape of a spiral. A magnet 382 is attached to thesupport 384 in close proximity to the force coil. In this manner, whenthe current is passed through the force coil, electromagneticinteractions between the force coil and the magnet will apply a force tosupport 370. Since support 370 is integral with arm 362 and both areattached to the support 384 through hinge 374, the force so applied tosupport 370 will also be applied to the arm. In other words, the magnetand the force coil serve the same functions as the ferromagnetic tip 57and solenoid coil 51 of U.S. Pat. No. 5,309,755.

The sensor 400 has a thickness of about 0.1-0.2 mm, except for thehinges. Arm 362 is about 15 to 16 mm long. The hinges 374 are about 0.02mm thick. The arm-support-hinge assembly has a resonance frequency ofabout 1 to 50 kHz.

FIG. 12 is a top view of a portion of a fine stage to illustrate oneembodiment of the fine stage 70 employing piezoelectric stacks. As shownin FIG. 12, this embodiment 300 of the fine stage includes a supportframe 402 and a moving frame 404 connected or attached to the sensorassembly 60. The moving frame 404 is connected to the support frame bymeans of four piezoelectric stacks 406 a, 406 b, 406 c, 406 d as well aseight flexure hinges 408. The piezoelectric stacks 406 a, 406 c are usedto move the moving frame 404 along the positive or negative X axisrelative to support frame and piezoelectric stacks 406 b, 406 d are usedto move the moving frame along the positive or negative Y axis withrespect to the support frame. Using piezoelectric stacks in thisconfiguration is advantageous over the use of piezoelectric tubes inthat the piezoelectric stacks cause relative motion between the movingframe and the support frame in the X-Y plane with minimal error in the Zdirection. Thus by using piezoelectric stacks, motion out of the X-Yplane may be less than 5 arcs in some cases. Capacitance sensors (notshown) may be used to sense any cross-talk or non-linearity of the stageand fed back to fine stage control 110 of FIG. 2 to correct for thecross-talk or non-linearity. The reduction of error in the Z directionreduces the complexity for a separate sensor for sensing motion in the Zdirection as well as feedback control of motion in the Z direction. Asuitable device using piezoelectric stacks for X-Y positioning is theP-730, or P-731 from Physik Instrumente (PI) GmbH & Co., Waldbronn,Federal Republic of Germany.

Mode of Operation

Some of the modes of operation have already been described above. Thus,the dual stage scanning instrument may be used like a conventionalstylus profilometer by deactivating the fine stage altogether.Alternatively, the dual stage scanning instrument may be first used as astylus profilometer to find an area of interest. Then the fine stage aswell as the coarse stage are both activated for causing relative motionbetween the sensor assembly and the sample. As noted above, in order toretain the fine resolution of the fine stage in X-Y positioning, it isdesirable to use the fine stage to cause relative motion in between thesensor assembly and the sample in a direction orthogonal to that causedby the coarse stage.

Where it is desirable to obtain a height profile of a surface of asample, the above-described mode where the fine stage causes relativemotion in a direction orthogonal to that caused by the coarse stage maybe controlled in order to cover any desired area of the surface of thesample. This is illustrated in FIG. 13. As shown in FIG. 13, the finestage is controlled to cause relative motion between the sensor assemblyand the sample along the Y axis and a coarse stage causes such relativemotion along the X axis.

While the controls 110, 112, 114, 116, and 120 of FIG. 2 may beimplemented using analog circuits, in the preferred embodiment, thesecontrols are implemented using digital circuits. In such event, motorsor position actuators are used in the fine and coarse stages to causerelative motion between the sensor assembly and the sample in discretesteps. As shown in FIG. 13, the motor for accomplishing fine stagemotion is controlled at a much higher frequency compared to that forcontrolling coarse stage motion, so that the resulting relative motionof the sensor assembly relative to the sample is along a zigzag path asshown in FIG. 13. Also as shown in FIG. 13, the two stages arecontrolled so as to cause the relative motion between the sensorassembly and the sample to be along a zigzag path 450 that oscillatesabout a line 452 at a substantially constant amplitude, so that thezigzag path 450 covers a substantially rectangular area. Alternatively,the two stages may be controlled so that the zigzag path covers an areathat is not rectangular in shape. The manner of controlling the twostages so that the zigzag path covers areas of other shapes is known tothose skilled in the art and will not be explained in detail here.

As noted above, one or more parameters of the sample may be sensed whilerelative motion is caused between the sensor and the specimen by meansof both the fine and the coarse stage. The sensor may be operated at asensing rate which is independent of the speed of relative motionbetween the sensor assembly and the sample by the two stages. Morespecifically, where the two stages cause relative motion at one or morefrequencies, the sensing rate of the sensor is independent of suchfrequencies and may be asynchronous with respect to such frequencies.The sensor may be used to sense the one or more parameters when thecoarse stage causes relative motion in one direction and the fine stagedoes not cause relative motion in such direction. Alternatively, thesensor may be used to sense the one or more parameters when the finestage causes relative motion in another direction and a coarse stagedoes not cause relative motion in such direction.

In one particular operational mode, one or both stages may be used tocause relative motion between the sensor assembly and the sample untilthe sensor assembly is in a predetermined position relative to a surfaceof the sample and this defines the initial imaging position. Thenrelative motion between the sensor assembly and the sample is caused sothat the sensor assembly moves in an initial direction substantiallyparallel to the surface of the sample to scan the surface. In a contactmode, such as when sensing of the height variations of the surface ofthe sample is desired, the predetermined position of the sensor assemblyrelative to the sample is such that the stylus tip of the sensorassembly is in contact with the surface of the sample to be measured orsensed. In a non-contact mode, such as where the parameter of the sampleother than height variation is to be sensed, the predetermined positionis such that the sensor assembly is not in contact with the sample. Ineither the contact or the non-contact mode, the fine and coarse stagecontrols may be operated in a constant force mode where the output ofthe deflection sensor 168 is fed back to the force control 166 in FIG. 6so that a constant force is applied between the stylus tip 164 and thesurface of the sample. Alternatively, in both the contact andnon-contact modes, this feedback may be turned off or set to a verysmall value in a constant height mode.

In yet another useful operational mode, either one or both of the fineand coarse stages may be used to cause relative motion so that thestylus tip 164 and the sample surface move toward each other. Thismotion can continue after the stylus tip is in contact with the surfaceof the sample to measure the compliance of the surface. Using themagnetic biasing scheme of FIGS. 4A-4D above, by increasing currentapplied to the force coil, the stylus tip is deflected towards thesample surface. A plot of the force versus the deflection of the armindicates the amount the surface reacted relative to the force appliedto it. If the surface is plastic and soft, the same force will cause alarger deflection compared to a hard surface and vice versa.

By using the secondary sensor to measure one or more parameters otherthan height variations of the sample surface at locations of the surfaceof the sample interacting with the stylus tip 164, it is possible to usethe scanning instrument of this application to sense substantiallysimultaneously the height at one or more locations of the surface andanother parameter of the specimen at the one or more locations. This canbe done with or without using both the fine and coarse stages. In otherwords, it is possible to use either just the coarse stage, or just thefine stage, so as to place the sensor assembly at particular locationsrelative to the surface of the sample in order to measure both theheight and one or more other parameters at such location of the surface.

The following description, related to a method for searching features ofa surface, is taken from the companion application; such descriptionrefers to FIGS. 14-25.

FIG. 14 illustrates a system for locating and measuring a feature ofinterest of a surface of a sample to illustrate the invention of thecompanion application. As shown in FIG. 14, system 1020 includes ascanner head 1022, a sensor 1024, and a stylus tip or probe tip 1026 forsensing the feature of interest 1030 on the surface 1032 of a sample1034. The position of the probe 1026 is controlled by a precisioncontrol block 1036 which is controlled by a system control 1038. System1020 may be a profilometer of the type described in U.S. Pat. No.5,309,755 to Wheeler. In such event, probe 1026 remains in contact withthe surface 1032 and moves up and down when the topology of the surfacechanges as the tip is moved across the surface. Sensor 1024 then sensesthe changes of position of the tip of probe 1026 in order to measure thetopology of the surface 1032.

System 1020 can also be a scanning probe microscope, in which case theprobe 1026 may or may not be in contact with surface 1032. Rather, theprobe 1026 is maintained at a predetermined distance from or in contactwith surface 1032 by moving the scanner, sensor and probe up and down bymeans of a feedback signal. The change in the feedback signal then givesan indication of the topology of the surface 1032. One type of scanningprobe microscope is illustrated in U.S. Pat. No. 4,724,318. The sensor1024 can also be a capacitance, magnetic force, van der Waals,electrical resistance, or current sensor for sensing parameters inaddition to the topology or topography of the surface. In such manner,even though a feature of interest may not be detectable optically, aslong as the feature exhibits other detectable characteristics such asmagnetic force, electrical capacitance or resistance, or van der Waalstype forces, the feature can still be located and measured.

FIG. 15 is a schematic view of a target area of a surface having afeature of interest 1030 to illustrate the invention of the companionapplication. First, a target area 1040 on the surface is designated.When the dimensions of the feature to be located are known, it may bedesirable to scan the probe 1026 along lines that are substantiallyparallel, where the spacing d between adjacent lines is less than theexpected dimensions of the feature to be sensed as illustrated in FIG.15. As shown in FIG. 15, probe 1026 may be scanned along seven scanlines where the separation d between adjacent scan lines such as 1042and 1044 is less than the expected dimensions of the feature. In FIG.15, the separation (d) is about 75% of the expected dimensions of thefeature. The spacing is chosen to maximize throughput but withoutcausing the scan to miss the feature. Preferably, such spacing is in therange of 50 to 85% of the expected dimensions of the feature.

For many features of interest, it may be important not only to locatethe feature, but also a center of the feature. Thus, for tungsten plugs,vias or clusters of and electrical conductive material, bumps or valleyson the surface of a textured hard disk, or pull tip recessions of aread/write head, it is useful or sometimes important to detect thecenter of such features and perform the measurement having the probe atthe center of the feature. FIG. 16 is a schematic view of window ortarget area 1140 of a surface having a feature 1030 thereon or thereinto illustrate a searching method for locating the center of the feature.As shown in FIG. 16, the probe tip is first scanned along the scan linesegment 1052(1), followed by scanning along line segment 1052(2), scanline segment 1052(3), and additional line segments if necessary, wheresegments 1052(2), 1052(3), and the additional line segments aresubstantially parallel to segment 1052(1). When the probe is scannedalong such line segments, sensor 1024 is used to sense the feature 1030,be it topology, electrical resistance or capacitance, magnetic force,van der Waals forces, or other features with detectable characteristics.Thus, when the tip of probe 1026 is scanned along scan line segment1052(3), sensor 1024 senses the feature 1030. Sensor 1024 not onlysenses the presence of feature 1030, but also the boundary points A, Bof feature 1030 along the scan line segment 1052(3) and sends its outputto system control 1038 to so indicate.

Once the sensor 1024 senses the presence of feature 1030, system control1038 instructs position control circuit 1036 to stop the scanning motionalong scan line segment 1052(3) even though some parts of the area 1140remains unscanned. The boundary points A, B are noted and the mid-pointC between points A, B is determined, and system control 1038 andposition control 1036 cause the scanner 1022 to scan along scan linesegment 1052(4) instead where the scan line segment 1052(4) passesthrough point C and is transverse to the scan line segments1052(1)-1052(3). The sensor 1024 senses the boundaries D, E of thefeature 1030 along the scan line segment 1052(4). Then the mid-point Oof the portion of the line segment 1052(4) between points D, E isdetermined to be the center of feature 1030 and the controls 1036, 1038cause the scanner 1022 to move the probe along scan line segment1052(5), that is, through the center O of the feature 1030, in order tomeasure the feature. System control 1038 records the output of sensor1024 and determines the locations of points A, B, C, D, E, and O. Theboundary points A, B, D, E may be found by sensing variations in thefeature over the surface.

Where it is not important to determine the center of the feature and tomeasure the feature at its center, the above searching process may beterminated after the feature 1030 has been found when scanning alongscan line segment 1052(3). The feature can simply be measured, such asat point C.

From the above procedure, it is evident that the searching method of theinvention of the companion application is superior to the conventionalsearch technique. Since no optical system separate and apart from system1020 is used for locating the approximate location of feature 1030, thesearching method of the invention of the companion application is notlimited by the resolution or power of a optical system employing one ormore lenses. Since the instrument for measuring the feature is used alsofor locating the feature, the method of the invention of the companionapplication avoids the need to locate the measuring probe and sensorrelative to the feature after the feature has been located. Furthermore,there is no need to acquire data over the entire target area 1140 beforethe location of the feature can be accurately determined. Instead, oncethe feature has been discovered, there is no need to scan the remainderof the unscanned portion of the target area and the user can proceedimmediately to measure the feature. This greatly improves throughput andavoids wasting the user's resources.

The advantages of the invention of the companion application can be seenmore clearly by reference to a concrete example. The feature of interestis an object of one micron diameter. Assuming that it is possible tofirst identify the feature to an accuracy of plus or minus two microns.This means that the object can be located initially at best to within atarget area of four microns by four microns. One can then scan thistarget area along scan line segments of length of four microns along thex direction and moving the probe 1026 in the y direction by an offset of0.75 microns each time until one of the scan lines crosses the object ofinterest. This means that a maximum of 5 scan lines are required tocross the object in FIG. 17. Once the scan line crosses the object ofinterest, then similar steps as those described above in FIG. 16 can betaken to determine the apparent center of the feature. This means thatafter a maximum of six scans, the center of the object is located andthe measurement of the feature can proceed. Even if the scan time ofeach of the four micron scan line segment amounts to one second, themaximum time required from the six scans with overhead can be of theorder of ten seconds. In contrast, in order to acquire 256 data pointson each of 256 scan lines at a rate of one line per second over a fourmicron by four micron area, such procedure would require four and onehalf minutes, where the data points on all but one of the 256 scan linesare wasted.

FIG. 18 is a representative cross-sectional view of a feature of thesurface to illustrate the invention of the companion application.

FIGS. 19A-19I are schematic views of a target area of a surfacecontaining a feature and search scan segments to illustrate anembodiment of the invention of the companion application. As before, atarget area 1040′ of a surface is defined that is known to contain thefeature of interest 1030′ to be located and measured. Two directions forscanning are defined with scan line segments 1062 along the firstdirection and scan line segments 1072 along the second direction. Thefirst and second directions are transverse to each other. As shown inFIGS. 19A-19I, the target area 1040′ is on a surface which is not planarand the scan line segments 1062 and 1072 are curved line segments ratherthan straight line segments. Nevertheless, the same searching method canbe employed to locate the feature 1030′ of the surface. Thus, as shownin FIG. 19D, the feature 1030′ is found when tip 1026 is scanned alongscan line segment 1062 a. Again, the boundary points A′, B′ sensed bysensor 1024 are recorded by system control 1038 and a mid-point C′between point A′, B′ along segment 1062 a is determined and the probe iscaused to scan along scan line segment 1072 a in the second direction.System control 1038 then records the boundary points D′, E′ sensed bythe sensor 1024 and the mid-point O′ between points D′, E′ along segment1072 a is determined to be the apparent center of feature 1030′ as shownin FIG. 19E. Then the probe is caused to scan along scan line segment1062 b where the feature 1032′ is measured by sensor 1024 as shown inFIG. 19F.

FIG. 19G illustrates the scanning method where it is adequate to locatethe feature without necessarily finding a center of the feature. In suchevent, the search can be ended after the feature is found. The featurecan then be measured upon ending the search without having to furtherscan the surface. Alternatively, the feature can be measured along scanline segment 1072 a in FIG. 19G. Where the feature is symmetrical, asshown in FIG. 19H, the center of the feature is, in some applications,more meaningful and it can be important to measure the feature at suchcenter.

FIG. 19I illustrates the search method for a substantially rectangularwindow on a flat surface. FIGS. 20A-20C are schematic views of a targetarea of a surface having a feature of interest and of scan pathsoperated in different modes, including non-contact, intermittent contactand contact modes to illustrate the invention of the companionapplication. FIG. 20A is a schematic view of a target area and a scanpath illustrating the intermittent contact mode. As shown in FIG. 20A,the tip of probe 1026 is scanned along scan line segments 1162 a, 1162b, 1162 c, and 1162 d, where these scan line segments are substantiallyparallel to one another. As shown in FIG. 20A, the tip of probe 1026proceeds across the surface 1040′ along each scan line segment in anintermittent mode. In the case of scan line segment 1162 a, the probeproceeds first without contacting the surface, such as along portion1162 a′ of the segment 1162 a. Then the tip is dropped down towards thesurface 1040′ until it contacts the surface along portion 1162 a″, andthen the tip is dragged along in substantially constant contact withsurface 1040′ along portion 1162 a′″. The tip is then again lifted fromthe surface along portion 1162 a″″ and then the above-described cycle isrepeated as the tip is moved across the surface 1040′ to trace out thescan line segment 1162 a. The other three scan line segments 1162 b,1162 c, 1162 d are scanned by the tip in a similar manner. The advantageof an intermittent scan described above is that, in some applications,it speeds up the scanning process in comparison with an operation modewhere the tip of the probe is in constant contact with the surface. Thismode of operation also reduces possible damage to the probe tip and/orthe surface due to frictional forces between the probe tip and thesample. The same is true for the non-contact mode in comparison to theintermittent contact or contact mode.

As before, the feature 1030′ is sensed when the probe tip is scannedalong scan line segment 1162d and the boundary points A′, B′ are notedand the mid-point of the portion of the line segment between points A′,B′ is noted and the probe tip is caused to be scanned along scan line orpath segment 1162 e transverse to the other scan line segments as beforeto locate boundary points D′, E′ so as to locate the center of thefeature 1030′ as before.

In some applications, it is advantageous to change the mode of operationafter the approximate location of the feature has been found. Thus,where the feature to be sensed has two different characteristics thatcan be sensed differently, a first characteristic can be used when thesurface is scanned to discover the approximate location of the feature,such as during scan paths 1162 a-1162 d. Then after the approximatelocation of the feature has been located, the user can switch to adifferent operational mode for sensing the center of the feature. Thenthe feature can be measured by means of either one of the twocharacteristics or any other characteristic that the feature may have.In many applications, however, it may be adequate to employ the sameoperational mode to find the approximate location of the feature as wellas the center of the feature and use a different operational mode whenthe feature is actually measured. This is illustrated in FIGS. 20B and20C.

As shown in FIG. 20B, the approximate location of feature 1030′ is foundwhen the surface 1040′ is scanned using the probe tip along scan linesegments 1162 a, 1162 b, 1162 c, and 1162 d in intermittent contactmode. The boundary points A′, B′ are noted and the surface is scannedalong scan line segment 1162 e to find boundary points D′, E′, and thecenter O′ in the same manner as that described above in reference toFIG. 20A. After the center O′ has been located, however, system 1020 isthen caused to operate in a contact mode where the tip of probe 1026 iscaused to contact surface 1040′ when it is scanned along scan linesegment 1162 f′ through the center O′ to measure the feature.

In FIG. 20C, the boundary points A′, B′, D′, E′, and the center O′ offeature 1030′ are first located by scanning the tip of probe 1026 alongscan line segments 1182 a, 1182 b, 1182 c, 1182 d, and 1182 e in amanner similar to that described above in reference to FIG. 20B, exceptthat when the probe tip is scanned along segments 1182 a-1182 e, theprobe tip is not in contact with surface 1040′. After the center O′ offeature 1030′ is located, system 1020 then is caused to operate in anintermittent contact mode along scan line segment 1182 f, to measure thefeature. Obviously, instead of measuring the feature through anintermittent contact mode along scan line segment 1182 f as shown inFIG. 20C, it is also possible to measure the feature using non-contactor contact operational modes along such scan line segment. Similarly, inFIG. 20B, it is also possible to measure feature 1030′ through anintermittent contact mode or non-contact mode. Such and other variationsare within the scope of the invention of the companion application.

Different modes are appropriate for different measurements. For example,to find magnetic or electrical variations, it may be appropriate to useintermittent or non-contact modes. For precise geometric measurements,contact or intermittent contact mode may be more desirable. The featurecan have a measurable magnetic characteristic as well as a roughsurface. It can be located by in the non-contact mode and its roughnessmeasured in the contact mode. But if such feature is very rough, it maybe desirable to measure it in the intermittent contact mode instead toavoid damage to the tip or surface to avoid frictional effects inherentin a constant contact technique.

The scanning speed during the intermittent contact mode can also befaster than that in the contact mode. Then after the feature has beenlocated and its center identified, the feature, such as its profile orgeometry can then be measured through an operational mode different fromthat used in locating the feature and its center if desired ornecessary. Thus, when measurement of the geometry or profile of thefeature is desired, system 1020 would then be operated in either thecontact mode or the intermittent contact mode.

In some applications, it may be desirable to be able to locate theboundaries and/or the center of the feature more accurately. For suchapplications, it may be desirable to repeat the above-describedsearching process, but at a finer resolution. This is illustrated inFIG. 20D. As shown in FIG. 20D, the target area 1040″ of the surface isfirst scanned by means of the probe tip along scan line segments1192(1), 1192(2), and 1192(3), where the approximate location of feature1030″ is discovered during the scan along 1192(3). Then a smaller targetarea 1040″ is defined to enclose the feature 1030″ and the searchingprocess is repeated along scan line segments 1194(1), 1194(2) . . . ,where the spacing between adjacent scan lines is smaller than thatbetween the scan lines 1192(1), 1192(2), and 1192(3). If desired, theentire target area 1040″ may be scanned to locate the boundary points ofthe feature more accurately. If different boundary points such as A″,B″, A′″, B′″ are taken into account for determining the location fortransverse scan 1196 than just the midpoint corresponding to only twoboundary points such as A″, B″, the center of feature 1030″ can be moreaccurately located. For example, a more accurate location can beidentified by taking an average position between the midpointcorresponding to boundary points A″, B″ and the midpoint correspondingto boundary points such as A′″, B′″.

In order to measure the profile or geometry of a surface, in referenceto FIG. 21A, system 1020 lifts the probe tip by a predetermined distance(h) from the surface, record the lateral distance (δx) traveled by thetip before it is lowered again to touch the surface and record thedistance by which the probe tip has been lowered before it touches thesurface again. Preferably, the tip is again lifted from such point ofcontact by the distance (h) moved laterally by distance (δx), loweredagain to touch the surface, and the distance that the tip is loweredagain recorded. This process is then repeated until the scan across thetarget area is completed. A record of such distance (δx) and thedistances that the tip is repeatedly lowered before it touches thesurface in the intermittent contact mode throughout the scan will givean indication of the geometry or profile of the surface.

In the embodiment of FIG. 21A, the probe tip is lifted after it islowered to touch the surface 1200, without dragging the probe tip alongthe surface. In other words, the probe tip is caused to gently tapsurface 1200 before it is lifted and the probe tip is not movedlaterally across the surface while it is contact with the surface. Insome applications, it may be desirable to drag the probe tip along thesurface after the tip is lowered to touch the surface, in an embodimentillustrated in FIG. 21B. After the probe tip has been dragged along thesurface 1200 for a predetermined distance, the probe tip is again liftedby a predetermined distance, such as h, moved laterally by apredetermined distance, and then again lowered to touch the surface1200. After the tip touches the surface, the tip is again dragged alongthe surface for a predetermined distance and the above-described processrepeated until a scan across the entire target area is completed asbefore. In the operational mode of FIG. 21B, in addition to recordingthe quantities h, δx and the distances by which the tip is repeatedlylowered before it touches the surface in the intermittent contact modethroughout the scan, system 1020 also records the change in height ofthe probe tip when the tip is dragged along the surface 1200. Suchinformation, in conjunction with h, δx, and the distances by which thetip is lowered before it touches the surface, will give an indication ofthe geometry or profile of the surface when system 1020 is operated inthe mode indicated in FIG. 21B.

Yet another operational mode of system 1020 in the intermittent contactmode is illustrated in FIG. 21C. Such mode is similar to that in FIG.21A, where in the operational modes of both FIGS. 21A and 21C, the probetip is not moved laterally to drag the tip across the surface after thetip is lowered to touch the surface, but is lifted to a predeterminedheight (h). However, instead of moving the probe tip up and down andlaterally along substantially straight lines as in FIG. 21A, the tip inFIG. 21C is moved along a more or less sinusoidal path across surface1200 until it scans across the target area. Such and other variationsare within the scope of the invention of the companion application.

A number of different: types of features can be located and measured inthe manner described above. In the semiconductor industry, it isfrequently desirable to locate a tungsten plug, or a metal cluster, ormetal filled via hole, for measurement of a specific geometric,magnetic, or electrical parameter. Thus, the tungsten plug, metalcluster, or via hole filled with a metallic material may be located bysensing for changes in capacitance, magnetic fore, electricalresistance, or geometric properties of the site. Thus, when system 1020is operated in a non-contact operational mode, where the tip is held ata small distance above the surface and scanned at a high speed over thesurface along a search pattern, the sensor 1028 senses changes incapacitance, tunneling current, or magnetic parameter (e.g. magneticforce experienced by the probe tip and sensor 1024) of the surface. Thechange in capacitance, tunneling current, or magnetic force may indicatelocation of a tungsten plug, metal cluster, or via hole filled with ametal. Once this location is determined, the stylus or probe can bebrought into contact or close proximity to the surface to measure theelectrical, magnetic, or geometric properties of the site.Alternatively, system 1020 may be operated in an intermittent contactmode and the resistance, capacitance, or magnetic parameter of thesurface is sensed at scanned locations by sensor 1024. When theresistance, capacitance, or magnetic parameter changes, this mayindicate the location of the tungsten plug, or metal cluster, or viahole. For example, the change in resistance may be indicated by thechange in the amount of current flow between the stylus tip and thesurface. If the amount of current flow increases, it may mean that thestylus is either at or at close proximity to a tungsten plug, metalcluster, or via hole. When the tip is in contact or in close proximityto the plug, cluster, or via hole, maximum current can be expected topass. Also when the spacing between the tip and the plug, cluster, ormetal filled via hole is decreased, the capacitance between the probetip and the surface is also decreased, because the dielectric effect ofspace between the surface and tip decreases with the spacing. When thetip is moving closer to the feature such as a plug or cluster made of amagnetic material or via hole filled with such material, the magneticforce between the probe tip and the feature may also increase until amaximum value when the feature and tip are in contact. This allows theuser to locate the plug, cluster, or via hole. After the plug, cluster,or via hole has been located, the electrical, optical, magnetic, orgeometric characteristic of the feature can then be measured. Theabove-described effects may be detectable and the features can be sensedin the contact, intermittent contact, or non-contact mode.

The above description applies to a process of locating and measurementof a magnetic feature by means of a magnetic parameter such as magneticforce. This can be performed by means of a magnetic force microscopewhich measures the magnetic force exerted between the sensor 1024 and afeature of a surface, such as a magnetic domain. Such magnetic domainmay be a pole tip recession on a magnetic read/write head. Such magneticforce microscope may employ an atomic force microscope or a profilometerin AC or DC modulation modes as described in known magnetic microscopeapplications. Magnetic force microscopy is described by P. Grütter, H.J. Mamin and D. Rugar in Springer Series in Surface Science, Vol. 28,entitled “Scanning Tunneling Microscopy II”, Eds. R. Wiesendanger and H.J. Güntherodt, published by Springer-Verlag Berling Heidelberg 1992, pp.152-207.

Another characteristic of a parameter that may be used to locate afeature is tunnelling current between the feature and the probe tip. Forexample, a metal cluster on a semiconductor surface may have a radicallydifferent current tunnelling characteristic to the probe than thesemiconductor surface.

Still other possible features that may be located and measured by meansof the invention of the companion application are unfilled via holes andsurface umps or valleys on laser textured hard disks. The uniformity insize of these bumps and valleys is a key factor in the manufacture ofhard disks. There may also be a variety of different sizes and shapes ofthese bumps on the disks. The bumps may have a donut shape or beasymmetrical about one or more axis. The pattern of such textured disksis generally known and the user is usually interested in measuring somekey features of several of these bumps around the disk. This means thatexact positioning of a bump or valley under the probe tip or stylus formeasurement is desirable. The bumps can vary in size from 1 to 10microns in lateral dimensions and a height of 100 to 1,000 Angstroms.The approximate locations of such bumps and valleys and the centers ofsuch bumps and valleys may be located by means of the methods describedabove, in particular the methods described in reference to intermittentcontact and contact modes for locating a geometric feature. Whereintermittent contact mode is employed, the values of δx and height (h)employed in reference to FIGS. 21A-21C are chosen so that it is unlikelyfor the probe tip to “jump over” the bump or valley. A suitable rangefor h may be 10-1,000 Angstroms, and a suitable value for δx may be afraction of the expected size of the feature or object. Thus, the bumpsmay have a donut shape of 5 micron diameter with a protrusion at thecenter of the donut. Of interest are the diameters of the bump along twoorthogonal axes in the plane of the surface about the center of thebump, the height of the lip (the protrusion at the outer perimeter ofthe laser bump) of the bump and the height of the raised protrusion atthe center of the bump relative to the non-textured area in a closevicinity of the bump.

Where it is desirable to locate a step on a surface, the user may wishto find the approximate location of the step by moving the probe tip inan intermittent contact mode. After the approximate location of the stephas been found, the user may wish to rescan such approximate location ina contact mode. After the location of the step has been found, the usermay lift the probe tip or stylus off the surface by a known distanceuntil it clears the step, moves it laterally over the step and thenlowers the tip across the surface until it touches the top of the step.The difference between the distance that the tip has been lifted and thedistance that the tip has been lowered yields an indication of theheight of the step. Alternatively, after the location of the step hasbeen found, the probe tip may be caused to move across the surface atthe step in contact mode, with the probe tip scaling or climbing thestep by means of a sideways sensor. Once the step is sensed, the sensorcan be used to measure the topography of the sidewall of the step or atrench, or a tungsten plug or a via hole by means of a sideways sensingtechnique such as that described in U.S. Pat. No. 5,347,854.

Other features of a surface that can be located and measured by means ofthe invention of the companion application include rough spots on asmooth surface or a smooth spot on a rough surface. The operating system1020 in a contact mode or an intermittent contact mode such as shown inFIG. 21B can be used employing a friction sensor to sense the change infriction between the probe tip or stylus and the surface. A suitablefriction sensor is described by M. Hipp, H. Bielefeldt, J. Colchero, O.Marti and J. Mlynek in “A Stand-alone Scanning Force and FrictionMicroscope”, Ultramicroscopy, 42-44(1992), pp. 1498-1503, ElsevierScience Publishers.

In the description above, the probe tip is scanned along scan linesegments that are substantially parallel to one another. This is,however, not required and other search paths are possible as illustratedin FIGS. 22, 23, and 24.

Instead of scanning the probe tip along substantially parallel scanlines, the feature 1030′ in window 1040′ of the surface may be locatedby means of a substantially random positioning scheme illustrated inFIG. 22. First a grid mesh 1198 is superimposed on the window 1040′. Thesize of the grids in the mesh is selected to be smaller than theexpected size of the feature or object of interest to be located. Forexample, the grids may have dimensions that are within 50% to 85% of theexpected size of the feature or object of interest. As shown in FIG. 22,a sequence of substantially random locations or positions a, b, c, d, e,f, . . . (where the sequence is not shown beyond location f in FIG. 22for reasons apparent below) at the grid intersection points 1199 isfirst generated within the window 1040′ of the surface, and system 1020causes the probe tip to be positioned sequentially at each one of thesepositions in the sequence specified: a, b, c, d, e, f, . . . . Asillustrated in FIG. 22, the probe tip senses for the first time thepresence of the feature 1030′ when it is placed or positioned inposition f. To discover more information about the feature at thispoint, it is more efficient not to follow the sequence of randompositions a, b, c, d, e, f, . . . beyond f but to follow a differentpositioning scheme. Instead, it may be preferable to then scan the probetip consecutively along two transverse directions. For example, theprobe tip may be scanned along two orthogonal directions X, Y in FIG. 22in order to locate the center of the feature in the manner describedabove in reference to FIGS. 19D-19F. Once the center of the feature hasbeen located, the probe tip is then scanned over such center in order tomeasure the feature.

In another embodiment, after the feature is discovered at location f bypositioning the tip at a sequence of random locations, in order to findout more information about the feature such as its boundary, the probetip may be moved along the +X, −X, +Y, −Y axis in any order in order tofind the boundary of feature 1030′ along the new axis. The boundary maybe found by sensing changes or variations in a parameter detected by thetip or sensor.

Thus, the probe tip may be first moved along the positive Y axis toposition 1 and then position 2 from position f to locate the boundary insuch direction. After the boundary in such direction has been discoveredwhen the probe tip moves from position 1 to position 2, it is discoveredthat position 2 is outside the boundary. The probe then may be moved toposition 3 which is along the positive X direction from position 1. Itis discovered that position 3 is within the feature and the tip is movedconsecutively to positions 4 and 5, discovering that both positions areoutside the feature, so that position 3 is at the boundary of thefeature. The tip is then moved in the −Y direction from position 3 toposition 6 discovering that it is still within the feature. The probetip is then moved to position 7, 8 along the X direction discoveringthat these are within the feature, and moved to position 9 along the Yaxis, discovering that it is outside the feature. It is then moved toposition 10, finding that it is within the feature. Therefore, anapproximation of the boundary of the feature can be obtained by drawinga line linking positions 1, 3, 6, 7, 8, 10. In a similar manner, theremaining portion of the boundary can be discovered and an approximationof such boundary indicated by drawing a line through positions 10, 13,16, 18, 20, 22, 24, 27, 29, and back to position 1. In theabove-described process, system 1020 will record the positions of thetip where sensing of the feature has been performed and the results ofsuch sensing.

Another method that can be used for locating the feature 1030″ on asurface is to scan the probe tip along a spiral path, such as in themanner illustrated in FIG. 23. As shown in FIG. 23, probe tip 1026 isscanned, beginning at position 1200 a path along the direction shown byarrow 1202. When the probe tip returns to the beginning position 1200,it then starts a spiral scan along path 1204. The spiral scan is suchthat adjacent portions of the scan path have different curvatures and,therefore, different angles of curvature. As illustrated in FIG. 23, forexample, the spiral path at position 1206 has a curvature angle of θwhereas the adjacent portion of the curve at position 1208 has an angleof curvature of φ, where φ is greater than θ. In other words, the angleof curvature increases as the tip moves along the spiral path, so thatthe probe tip zooms into a smaller and smaller area in order to locatethe feature. The change in angle of curvature is such that adjacentportions (such as portions at positions 1206, 1208) of the spiral pathare not spaced further apart by more than the expected dimensions of thefeature. As shown in FIG. 23, the probe tip senses the presence of thefeature at or close to position 1208. At such position, the angle ofcurvature of the spiral path is increased so that the spiral path wouldcover a smaller area than it otherwise would if the feature has not beenlocated. This will speed up the process of finding the boundaries of thefeature. The positions of the tip where boundary of the feature has beensensed (such as by sensing variation in a characteristic of the feature)are recorded to define more accurately the location of the feature.

Thus, in general, a predetermined scan path may be first adopted tolocate the approximate location of the feature. Once this has beenaccomplished, it may be advantageous to stop scanning along such path,and to scan the tip along a different path to find out more informationabout the feature. The above referenced predetermined path may be a setof substantially parallel scan line segments such as 1062 a in FIGS.19D-19G. Or it may be a sequence of substantially random locations inFIG. 22, or the spiral path in FIG. 23 from point 1200 to point 1208.After the feature has been located, it may be desirable to switch to adifferent scan path to more efficiently find out more information aboutthe feature. Thus, in FIGS. 19E-19I, 20A, 20B, 20C, the tip is scannedalong paths 1072 a, 1162 e, 118 2e, where information from prior scansare used to determine such paths. In FIG. 22 it may be scanned along theX, Y axes or along the path defined by positions 1, 2, 3, 4, . . .without using information about the prior scan path other than thelocation where the feature is sensed. In FIG. 23, it is scanned alongthe path beyond point 1208 using information about the angle ofcurvature of the prior scan path as a reference (to determine the newangle of curvature) as well as the location where the feature is sensed.

Instead of scanning the tip along a curved spiral path as in FIG. 23,the spiral path can be roughly rectilinear, as shown in FIG. 24. Asshown in FIG. 24, the probe tip is scanned along paths that spiral intowards a smaller area but along paths where adjacent portions of thepaths are substantially parallel to one another. Such and othervariations of the spiral path are within the scope of the invention ofthe companion application.

Instead of scanning the probe tip along parallel paths by startingalways from the same edge, the probe tip can also be scanned along aserpentine path 1250 as shown in FIG. 25. Scanning a probe tip along aserpentine path may reduce the amount of time required to scan the samelocations of the surface as compared to a scanning scheme where theprobe must return to the same edge of the target area before it isscanned across the surface to locate the feature.

The invention of the companion application has been described byreference to preferred embodiments described above. Various changes andmodifications may be made without departing from the scope of theinvention of the companion application. Thus, the feature can also bedetectable by means of its thermal characteristics, such as thermalconductivity by means of a temperature sensor. As another example, whilethe invention of the companion application has been illustrated byreference to features on the surface of samples, the same is applicableeven if the feature is inside the surface as long as characteristics ofthe feature can be sensed or detected, such as by electrical, magnetic,optical, thermal or other means.

The above section is taken from the companion application.

FIG. 26 is a schematic view of a conventional scanning probe microscopeuseful for illustrating the invention. As shown in FIG. 26, the scanningprobe microscope (SPM) includes a coarse X-Y stage 1502 a and a coarse Zstage 1502 b. The sample 90 is placed on stage 1502 a. The SPM sensor1504 is mounted onto a fine X-Y-Z stage 1506 which is, in turn, mountedonto stage 1502 b by means of block 1508. The conventional SPM 1500 canbe used to perform the scanning operation described below in referenceto FIGS. 30-34E.

FIG. 27 is a schematic view of a scanning instrument that includes bothan SPM sensor 1504 and a profilometer sensor assembly 60. Both sensorsor sensor assemblies are mounted onto a fine X-Y stage which may beanyone of the fine stages described above such as stages 70, 70′, 70′″,and 70″″. As in the embodiments of the dual stage scanning instrumentdescribed above, the fine stage 70-70′″ has a resolution much finer thanthat of the conventional X-Y positioning stage used for the stylusprofilometer so that positioning resolution can be much improved whileretaining all the advantages of the conventional stylus profilometer. Itis also advantageous over the SPM since the system 1550 retains many ofthe profilometers advantages, such as wide dynamic range in the Zdirection and long scan capability of the order of hundreds ofmillimeters.

Instrument 1550 may be controlled by means of the scheme illustratedabove in FIG. 2 in essentially the same manner as that described abovein reference to such figure. Either the SPM sensor 1504 or theprofilometer sensor 60 may be used, since both sensors are mounted onthe fine X-Y stage 70-70′″. Thus, fine stage control 110 may be used tocontrol the fine stage in FIG. 27.

FIG. 28 is a schematic view of a scanning instrument having both a SPMsensor and profilometer sensor, but where the SPM sensor is mounted ontoa SPM fine X-Y-Z stage (which is in turn mounted to block 134) but wherethe profilometer is not, to illustrate another embodiment of theinvention. In system 1600, since the profilometer sensor is not mountedonto a fine stage, only the SPM sensor may be used for sensing nanometeror subnanometer features, while the profilometer sensor can still beused for long scan profiling as in the conventional stylus profilometer.Both systems 1550 and 1600 may be used to perform the scanningoperations described below in reference to FIGS. 30-34E. Fine stagecontrol 110 may be used to control the fine stage 1506 in FIG. 28.

FIG. 29A is a profile of a surface such as that of a semiconductorwafer. As shown in FIG. 29A, the surface 1602 is bow-shaped. Via holesare present at points AA and BB. As noted above, conventional stylusprofilometers do not have the resolution to detect the local features ofholes AA and BB shown in FIGS. 29B and 29C, even though it is able todetect the bow-shaped profile of the surface. SPMs, on the other hand,are able to detect the local features of the via holes AA and BB, but isunable to either measure the profile 1602 or to give the relativeheights of the two via holes AA and BB. The invention of thisapplication is capable of locating both the overall profile of thesurface 1602, the local profile at points AA and BB at high resolution,as well as the relative height of the two via holes.

In order to obtain an overall global profile of a surface, a long scanis performed as shown in FIG. 30 along a first scan path 1612. Then anumber of short scans along scan paths 1614 may be performed either ator in the vacinity of the long scan path 1612 but at a higher resolutionthan that employed for the long scan so that nanometer or subnanometerfeatures illustrated in FIG. 29B and 29C can be measured. If the sameprobe tip of the profilometer or scanning probe microscope is used forscanning both the long scan path 1612 and the short scan path 1614, andthe data sensed correlated with the X-Y-Z position of the tip, therelative height and locations of local features such as via holes AA andBB shown in FIG. 29A can be determined. Even if the long scan along path1612 is taken with a probe tip which is different from that used for theshort scans along scan path 1614, as long as the relative positions ofthe two probe tips are known, it is still possible to correlate therelative height and positions of local features such as via holes thatare spaced far apart on the wafer surface. As noted in FIG. 30, theshort scans may be taken along directions which are not in parallel toone another or to the long scan path 1612. The long scan path 1612 mayhave a range of up to 500 milimeters. As the probe tip is scanning alongeither the long scan path or the short scan paths, a feature of thesurface either inside or on top of the surface are sensed by any one ofthe methods described above. Such features are sensed in a short scan ata resolution of 0.1 to 5 nanometers and a resolution of 5 to 10nanometers in directions parallel to the surface at (i.e. in the X-Yplane) and 1 to 5 nanometers in directions perpendicular to the surfaceof the sample (i.e. in the Z direction).

Thus, the feature sensed in reference to FIG. 30 may be a profile orother geometric parameter, or electrical, magnetic, optical, thermal,frictional, or van de Waals force parameter. If desired, the scanningsystem may be used to detect a different parameter in the short scanpaths 1614 than the one detected along the long path 1612. In fact,different parameters may be sensed in the different short scans 1614.

The scanning operation illustrated above in FIG. 30 may be performed bymeans of any one of the dual stage scanning instrument described above.To coarse Z stage 80 a and the coarse X-Y stage 80 b may be used formoving the sensor assembly and probe tip along the long scan path 1612and a fine X-Y stage may be used for moving the sensor assembly andprobe tip in the short scans. In system 1500, for example, the coarsestages 1502 a, 1502 b are used for causing relative motion betweensensor 1504 and sample 90 to scan the long scan path 1612 and the finestage 1506 may be used for causing such motion along short scan paths1614. In system 1550, coarse stages 80 a, 80 b are used for the longscan and fine stage 70-70′″ is used for the short scan. Either one ofthe two sensors 60, 1504 may be used in the long scan and the shortscans and different sensors may be used in the eight scans illustratedin FIG. 30. As long as the relative positions of the two sensors areknown, such as by attaching the two sensors so that they have a fixedposition relative to one another, the data obtained from all of thescans, long or short, as shown in FIG. 30 can be correlated. The scansalong the long scan path 1612 and short scan paths 1614 can be in anyone of a contact, non-contact, or intermittent contact modes asillustrated above. The short scan path may have a length less than 100microns long whereas the long scan path 1612 may have a length in excessof 100 microns long.

As shown in FIG. 30, the short scan path 1614 a does not intersect thelong scan path 1612. If it can be assumed that the topology of thesurface has not changed drastically in the distance between scan path1614 and 1612, then the data obtained in the scan path 1614 a can stillbe correlated with that obtained along the portion of the scan path 1612close to path 1614 a. Where the short scan path and the long scan pathintersect, the user may actually be able to correlate the data moreaccurately.

Each of the long scan paths 1612 as well as the short scan paths 1614may actually comprise a number of scan line segments, such as 1620 shownin FIG. 31. Where the scan path segment 1620 cover a substantial portionof the wafer surface, such scan path would enable the user to measurethe topography over a substantial portion of the wafer surface. Wherethe scan line segments 1620 are short, data acquired along such segmentswill reveal the topography in an area where a local feature such as avia hole is expected. In one embodiment, the segment 1620 aresubstantially parallel to one another. As shown in FIG. 32, it ispossible to scan from a starting point 1630 to end point 1632 along along scan and do short scans through points 1630, 1632. Preferably, theshort scan through point 1630 precedes the long scan and the short scanthrough point 1632 is done after the long scan.

In FIG. 30, the long scan is first performed followed by the shortscans. Where the locations of local features of interest are known, itmay be desirable to first perform a number of short scans, each througha corresponding feature of interest followed by a long scan taken overan area of the surface not over a particular feature of interest but ata location optimized for correlating the data obtained through the shortscans at each of the features of interest as illustrated in FIG. 33.Thus, short scans may first be performed through each one of the points1640. Thereafter, an optimized path 1642 may be selected to bestcorrelate the data obtained during the short scans through points 1640.In the preferred embodiment, a least square fit calculation may beperformed based on the locations of the point 1640 to select the optimalscan path 1642.

During any time in the scanning process, when the data from the scanningis analyzed in real time, the user may discover that it is desirable tolook for a particular feature at or in the vicinity of the surface. Insuch event, the searching process described above for a feature of asurface may be employed by determining a target area and searching thesurface by means of the probe tip within the target area to provide anindication of a feature of interest by detecting the feature. As aresult of such searching operation, a scan path may be selected as afunction of the indication. For example, if it appears that a recess isdiscovered in the searching operation, a scan path may be selected thatwill pass over such recess. As noted above, the searching process mayinvolve scanning the probe tip along substantially parallel search linesegments separated by a offset that is preferably less than the expecteddimensions of the feature that is being searched. As described above,after the approximate position of the feature has been found, it ispreferable to scan the tip along another search line segment transverseto the search line segments in the prior scans to locate the center ofthe feature of interest.

The scan paths, such as paths 1612, 1614, 1620, may comprise scan linesegments substantially parallel to one another, as spiral scan segmentor serpentine scan line segment such as illustrated in FIGS. 23 and 25.

FIGS. 34A-34E illustrate how data obtained from different scans can becorrelated. FIG. 34A is a profile of a surface with three local featuresCC, DD, EE. Local profiles of the three features are shown in FIGS.34B-34D respectively. As shown in FIG. 34A, the surface has a large arearecess with feature CC, EE on the two sides of the recess and feature DDat the bottom of the recess. By means of the process described above,the overall profile of the recess can be measured as well as the localfeatures CC, DD, EE at high resolution. The correlation of the localfeatures CC, DD, EE is shown in FIG. 34E, which shows the depth of thevia holes as well as the relative height of the three features.

While the invention has been described above by reference to variousembodiments, it will be understood that different changes andmodifications may be made without departing from the scope of theinvention which is to limited only by the appended claims and theirequivalents.

What is claimed is:
 1. An instrument for sensing a sample, comprising: a sensor for sensing a parameter of the sample; a coarse stage causing relative motion between the sensor and the sample; a fine stage causing relative motion between the sensor and the sample; and at least one controller controlling the two stages so that the relative motion caused by the coarse stage causes the sensing tip to scan across the surface of the sample when the sensor is sensing said parameter of the sample.
 2. The instrument of claim 1, said fine stage having a resolution of one nanometer or better.
 3. The instrument of claim 1, said coarse stage having a resolution of one micrometer or better.
 4. The instrument of claim 1, wherein the two stages are such that the instrument has a range of at least 500 micrometers in at least one direction when the sensor is sensing said parameter of the sample.
 5. The instrument of claim 1, wherein said sensor is a height sensor that measures directly the height variation of a surface of the sample.
 6. The instrument of claim 5, said sensor including: a stylus arm having a stylus tip; and a capacitance gauge.
 7. The instrument of claim 1, wherein said sensor senses thermal variations, or an electrostatic, a magnetic, a light reflectivity or a light transmission parameter of the sample, or the height variation of a surface of the sample.
 8. The instrument of claim 1, wherein said sensor senses substantially simultaneously the height at one or more locations of a surface of the sample and at least another parameter of the sample at said one or more locations.
 9. The instrument of claim 8, said sensor including a stylus tip that senses the height at one or more locations of a surface of the sample and a sensor element in the stylus tip or in the proximity of the stylus tip for sensing said at least another parameter.
 10. The instrument of claim 1, wherein each of the two stages causes relative motion between the sensor and the sample in XYZ three dimensional space, the coarse stage comprising an XY portion for causing relative motion between the sensor and the sample in a direction substantially parallel to a surface of the sample and a Z portion for causing relative motion between the sensor and the sample in a direction substantially normal to the surface of the sample.
 11. The instrument of claim 1, wherein said at least one controller controls the two stages so that both of the two stages substantially simultaneously cause relative motion between the sensor and the sample when the sensor is sensing said parameter of the sample.
 12. The instrument of claim 1, wherein said sensor comprise: a stylus arm having a stylus tip for sensing a surface parameter of the sample; a hinge supporting the stylus so that the stylus arm is rotatable about the hinge; and a device applying a force to the stylus arm.
 13. The instrument of claim 12, said stylus arm having a dynamic range of at least about 500 micrometers when rotated about the hinge. 